The present invention relates to N-phosphonomethylglycine guanidine derivative salts and herbicidal compositions including such salts.
N-phosphonomethylglycine (glyphosate) is well known as a highly effective, widely used and commercially effective herbicide useful for combating the presence of a wide variety of unwanted vegetation. Glyphosate in its strict sense is an acid compound, but the word “glyphosate” is used herein in a less restrictive sense to encompass not only glyphosate acid but also salts, adducts and esters thereof, and compounds of which are converted to glyphosate in plant tissues or which otherwise provide glyphosate ions. Glyphosate has three acid sites, and can therefore form tribasic salts. Monovalent glyphosate anions predominate at around pH 4. Divalent glyphosate anions predominate at about pH 7-8. Preferred aqueous compositions typically have a pH value not greater than about 8. At these pH values the fraction of glyphosate existing as a tribasic salt is negligibly small.
Glyphosate has low water solubility in free acid form, and is often formulated in commercial compositions in the form of a water soluble salt. Salts in commercial use include the ammonium salt, alkylamine salts, including the isopropylamine salts, alkali metal salts and the trimethyl sulfonium salts. Aminoguanidine salts of glyphosate are also common. Exemplary herbicidal salts of glyphosate are disclosed in U.S. Pat. No. 3,799,758 to Franz, U.S. Pat. No. 3,853,530 to Franz, U.S. Pat. No. 4,140,513 to Prill, U.S. Pat. No. 4,315,765 to Large, U.S. Pat. No. 4,405,531 to Franz, U.S. Pat. No. 4,481,026 to Prisbylla and U.S. Pat. No. 4,507,250 to Bakel. In most of these salts, the counterion to the glyphosate anion is a relatively low molecular weight, non amphiphilic cation.
Many commercial formulations of glyphosate salts utilize these low molecular weight, non-amphiphilic salts. Commercial formulations of glyphosate salts containing the isopropylammonium salt include Roundup®, Accord®, and Roundup Ultra® herbicides, all commercially available from Monsanto Company. Commercial formulations of glyphosate containing the ammonium salt include Roundup® Dry and Rival® herbicides, both commercially available from Monsanto Company. Commercial formulations of glyphosate containing the sodium salt include Roundup® Geoforce herbicide of Monsanto Company, and commercial formulations containing the trimethylsulfonium salt include Touchdown® herbicide commercially available from Syngenta.
Salts of glyphosate possessing higher molecular weight, amphiphilic cations have also been disclosed. These amphiphilic cations include those having a hydrophilic moiety such as ammonium, ethanolammonium, polyoxyethylene ammonium, or sulfonium group, and a hydrophobic moiety containing between 1 to 4 hydrocarbyl groups having in total more than 6 carbon atoms. For example, U.S. Pat. No. 4,405,531 discloses primary, secondary, and tertiary ammonium salts of glyphosate possessing an amphiphilic cation having a molecular weight less than 300. U.S. Pat. No. 5,668,085 discloses a salt in which the cations of the glyphosate salt are derived from the surfactant. Specifically, U.S. Pat. No. 5,668,085 discloses ammonium salts of glyphosate with amphiphilic cations derived from polyoxyethylene tertiary C8-22 alkylamine surfactants. U.S. Pat. No. 5,668,085 discloses as an example N-cocoalkyl-N,N-diethanolammonium salt of glyphosate where “cocoalkyl” refers to a mixture of predominantly C12 and C14 alkyl chains, derived from coconut oil.
Glyphosate is usually applied to foliage together with amphiphilic materials, particularly surfactants. Surfactants enhance the biological effect of glyphosate in a number of ways, not all of which are completely understood. When glyphosate is applied to foliage as a dilute aqueous composition by conventional hydraulic spraying, the presence of surfactant in the aqueous composition can generally increase the percentage of smaller spray droplets and decrease the percentage of large spray droplets. Smaller droplets tend to have lower momentum than larger droplets and are more likely to be retained on a foliar surface and less likely to rebound from that surface. Spray retention is also facilitated by adhesion between surfactant molecules in a spray droplet and the foliar surface which is typically waxy and hydrophobic in most plants. This adhesion also aids in preventing the rebounding of droplets from the foliar surface and the run-off of droplets from the foliar surface. Surfactants also tend to increase the area of contact between a spray droplet and the foliar surface and thereby tend to enhance penetration of glyphosate from the droplet into and through the cuticles of leaves to access internal plant tissues.
The basicity possessed by guanidines and guanidine derivatives has contributed to their use in a wide variety of applications, ranging from cleaning products to additives in cosmetics.